diff --git a/jni/com_android_bluetooth_hfpclient.cpp b/jni/com_android_bluetooth_hfpclient.cpp
index 030681f..e4d557c 100644
--- a/jni/com_android_bluetooth_hfpclient.cpp
+++ b/jni/com_android_bluetooth_hfpclient.cpp
@@ -567,18 +567,22 @@
 static jboolean sendATCmdNative(JNIEnv *env, jobject object, jint cmd,
                                 jint val1, jint val2, jstring arg_str) {
     bt_status_t status;
-    const char *arg;
+    const char *arg = NULL;
 
     if (!sBluetoothHfpClientInterface) return JNI_FALSE;
 
-    arg = env->GetStringUTFChars(arg_str, NULL);
+    if (arg_str != NULL) {
+        arg = env->GetStringUTFChars(arg_str, NULL);
+    }
 
     if ((status = sBluetoothHfpClientInterface->send_at_cmd(cmd,val1,val2,arg)) !=
             BT_STATUS_SUCCESS) {
         ALOGE("Failed to send cmd, status: %d", status);
     }
 
-    env->ReleaseStringUTFChars(arg_str, arg);
+    if (arg != NULL) {
+        env->ReleaseStringUTFChars(arg_str, arg);
+    }
     return (status == BT_STATUS_SUCCESS) ? JNI_TRUE : JNI_FALSE;
 }